Vehicles such as cherry pickers, cranes, backhoes and the like usually include a one or two piece boom. Before these vehicles are driven or transported, the boom is usually moved to a stowage position to prevent undue stress on the boom. However, the boom still has a tendency to bounce when the vehicle hits a bump or encounters a turn during transport. This causes significant stress on the joints where the boom is connected to the vehicle and on those portions of the boom which strike other parts of the vehicles. Therefore, it is necessary to secure the boom prior to transport of the vehicle.
Securement of the boom is usually accomplished by providing a boom rest which supports the boom when the boom is moved to its stowage position. Tie-down straps may then be manually wrapped from one side of the rest, around the boom, to the opposite side of the rest and securely tightened. This minimizes both vertical and lateral movement of the boom during transport. However, the boom rest is frequently located in a location which is difficult to reach, such as on top of the cab of the vehicle. Moreover, operators often forget to use such manual systems, which leads to an unnecessarily frequent number of instances in which the boom bounces out of the rest during transport and damages the boom or the vehicle. To eliminate this potential for operator error, it is desirable to provide a system for automatically latching a boom without additional action by the operator.
Several devices are known for automatically latching a boom. U.S. Pat. Nos. 2,423,583 and 2,699,314 discloses devices for automatically securing a boom mast on a cargo ship. However, these devices do not automatically align the boom with the latch and thus require additional operator intervention to provide such alignment. In addition, these devices require that the boom be manually unlatched before the boom can be moved to a use position.
U.S. Pat. Nos. 4,184,803, 4,273,502, 4,278,394 and 4,370,090 disclose a series of backhoe boom latches in which a ring is attached to the boom. The bottom of the boom is connected to the frame of the vehicle, and the boom pivots about a horizontal axis by a vertical pivot pin. When the boom is moved towards its stowage position, the ring slides over the top of the pivot pin until it surrounds the pin, and the ring then drops over the pivot pin. To release the boom, the ring may be manually lifted above the pin. However, movement of the boom towards a use position (whether by actuation of hydraulic controls or by bouncing of the vehicle during transport) may also cause the ring to be lifted from the pin. U.S. Pat. No. 4,636,132 discloses a variation on this concept. Instead of a ring dropping around a pin on the frame, a latch drops behind a slot in the pin when the boom is moved to its stowage position. Again, the latch must be manually released. These devices have several shortcomings. Most notably, none are positive latches, in that bouncing of the boom during transport can generate enough movement of the boom to unlatch it. Also, these latches only prevent horizontal movement of the boom, and not vertical movement. Additionally, these devices do not support the weight of the boom, which is an important factor in achieving boom stability during transport.
U.S. Pat. No. 4,674,638 discloses a system for dampening boom oscillation during transport by supplying hydraulic pressure to the boom's hydraulic cylinders. However, this system does not latch the boom.